In order to determine performance characteristic for a particular electronic device, certain environmental situations are simulated under controlled testing conditions. For example, an electronic device containing electrical components and circuits used in a telecommunications system are tested in an environmental chamber. The environmental chamber is capable of simulating temperature extremes as well as temperature ranges similar to those that actually exist out in the field where the equipment is deployed. Under these testing conditions, the telecommunication system is tested for Bit Error Rates (BERs) caused by the extreme temperature conditions as well as the temperature fluctuations.
Under these testing conditions, large fans are deployed in the environmental chamber, similar to the fans used in the field, to circulate the air around the equipment for rapid temperature changes. Typical testing conditions measure for or are based on measurements of circuit temperatures. As a result, the testing conditions typically do not accurately reflect the actual working conditions, especially when the electronic device is assembled in the field within a card assembly shelf. More specifically, actual assembly of the electronic device within the in the field is impacted by the relative position of the electronic device with respect to the location of the circulating fan. For example, if an equipment is tested in an environmental chamber in a position that is close to the fans that are used to circulate the air and then installed in the field in a position that is further from the fans, then the testing parameters under which the equipment is qualified or certified will not reflect the actual parameters under which the equipment is deployed. This is predominantly because the parameters under which the equipment is tested and certified is dependent upon temperature ratings, which can vary from one location in the rack assembly to another location due in part to the fact that heat dissipation is based on temperature of the ambient air as well as the rate of airflow.
The rate of heat dissipated from a circuit is a function of airflow velocity. Thus, when the card is installed in a rack for its intended use the airflow velocity may be less than the airflow in the environmental testing chamber. Thus, the conditions under which the circuit was qualified will not be the same as the conditions that actually exist in the field because of the changes in the airflow rate in certain areas; these areas are often referred to as “hot-spots”. Typically hot-spots occur when the airflow, which is induced by fans, varies significantly with the cross-section of the card cage or rack assembly. Equipment mounted in a rack may have large gaps between the top of the assembly and the bottom. Air will find the path of least resistance, which would be out of the front and or sides of the assembly rather than through the circuit components. For example, when an equipment that allows only side-to-side airflow is placed upstream from an equipment that requires vertical airflow, the air supply to the downstream equipment is choked. Thus, although the overall temperature reading in the field for any rack or chamber may be within the temperature limits that the circuit was qualified for, the BER may still exceed the limits that the equipment was qualified or certified at because the operating temperature of the chamber at the particular location of the equipment can actually exceed the qualification temperature due to the “hot-spots” caused by inadequate airflow velocity.
Therefore, what is needed is a system and method for qualifying electronic circuits based on airflow velocity in combination with temperature rating. Furthermore, what is needed is a system and method for measuring and monitoring the airflow velocity at various positions within the rack during operation in the field in order to determine the position of and eliminate hot-spots.